AIDS patients suffering from debilitating nerve pain got as much or more relief by smoking marijuana as they would typically get from prescription drugs -- and with fewer side effects -- according to a study conducted under rigorously controlled conditions with government-grown pot.

In a five-day study performed in a specially ventilated hospital ward where patients smoked three marijuana cigarettes a day, more than half the participants tallied significant reductions in pain.

By contrast, less than one-quarter of those who smoked "placebo" pot, which had its primary psychoactive ingredients removed, reported benefits, as measured by subjective pain reports and standardized neurological tests.

The White House belittled the study as "a smoke screen," short on proof of efficacy and flawed because it did not consider the health impacts of inhaling smoke.

But other doctors and advocates of marijuana policy reform said the findings, in today's issue of the journal Neurology, offer powerful evidence that the Drug Enforcement Administration's classification of cannabis as having "no currently accepted medical use" is outdated.

"This should be a wake-up call for Congress to hold hearings to investigate the therapeutic use of cannabis and to encourage more research," said Barbara T. Roberts, a former interim associate deputy director in the White House Office of National Drug Control Policy, now with Americans for Safe Access, which promotes access to marijuana for therapies and research.

Countless anecdotal reports have suggested that smoking marijuana can help relieve the pain, nausea and muscular spasticity that often accompany cancer, AIDS, multiple sclerosis and other ailments. But few well-controlled studies have been conducted.

The new study enrolled 50 AIDS patients with severe foot pain caused by their disease or by the medicines they take.

The team first measured baseline pain, both subjectively (patients ranked their pain on a scale of 1 to 100) and with two standardized tests, one involving a small hot iron held to the skin and another involving hot chili pepper cream.

Then, for five days, patients lit up at 8 a.m., 2 p.m. and 8 p.m. using a calibrated puff method that calls for inhaling for five seconds, holding one's breath for 10, then waiting 45 seconds before the next.

The cigarettes were kept frozen and locked in a safe, then thawed and humidified one day before use. Cigarette butts and other debris were collected, weighed and returned to the safe to ensure no diversion for recreational purposes.

Grown on the government's official pot farm in Mississippi, the drug was about one-quarter the potency of quality street marijuana. The inactive version was chemically cleansed of cannabinoids, the drug's main active ingredients.

"It smelled like and looked like" normal marijuana, said study leader Donald I. Abrams, a physician at San Francisco General Hospital, where the smoking ward was located. Like the patients, Abrams was not told who had the active pot until the study was over.

Thirteen of 25 patients who smoked the regular marijuana achieved pain reduction of at least 30 percent, compared with six of 25 who smoked placebo pot. The average pain reduction for the real cannabis was 34 percent, compared with17 percent for the placebo.

Opioids and other pills can reduce nerve pain by 20 to 30 percent but can cause drowsiness and confusion, Abrams said. And many patients complain that a prescription version of pot's main ingredient in pill form does not work for them.

That was true for Diana Dodson, 50, who received an AIDS diagnosis in 1997 after a blood transfusion.

"I have so many layers of pain I can hardly walk," said Dodson, who was in the new study. Prescription drugs made her feel worse. "But inhaled cannabis works," she said.

Patients in the study -- all of whom had smoked pot previously -- reported no notable side effects, though the researchers acknowledged that people unfamiliar with the drug may not fare as well.

Igor Grant, director of the University of California Center for Medicinal Cannabis Research, which funded the research, said the study was probably the best-designed U.S. test of marijuana's medical potential in decades. He called the results "highly believable."

But David Murray, chief scientist at the White House Office of National Drug Control Policy, called the findings "not particularly persuasive." The study was relatively small, he said, and it is likely that those who received the real pot were aware of that, introducing a bias of expected efficacy.

"We're very much supportive of any effort to ameliorate the suffering of AIDS patients," Murray said. But even if ingredients in marijuana prove useful, he added, they ought to be synthesized in a pill to make dosing more accurate and to minimize lung damage.

Separately, ending a six-year effort, a Massachusetts group learned yesterday that it had won a legal victory against the DEA in its battle for federal permission to grow its own cannabis for federally approved studies, instead of relying on government pot.

In an 87-page opinion, administrative law judge Mary Ellen Bittner ruled that it "would be in the public interest" to allow a University of Massachusetts researcher to cultivate marijuana under contract to the Multidisciplinary Association for Psychedelic Studies (MAPS), which sponsors medical research on marijuana and other drugs.

The DEA is not obligated to follow the advice of its law judges, but the detailed decision should make it difficult for the agency to balk, said MAPS President Rick Doblin.